Method for performing a harq operation in a carrier aggregation with at least one scell operating in an unlicensed spectrum and a device therefor

ABSTRACT

The present invention relates to a wireless communication system. More specifically, the present invention relates to a method and a device for performing a HARQ process in a carrier aggregation, the method comprising: configuring with a plurality of cells, wherein each of the plurality of cells belongs to one of a first cell group and a second cell group; receiving two sets of maximum number of Hybrid-ARQ (HARQ) transmission, wherein a first set is related to a first cell group and a second set is related to a second cell group; applying the first set to a HARQ process if the HARQ process is assigned to the first cell group; and applying the second set to the HARQ process if the HARQ process is assigned to the second cell group.

TECHNICAL FIELD

The present invention relates to a wireless communication system and,more particularly, to a method for performing a HARQ operation in acarrier aggregation with at least one SCell operating in an unlicensedspectrum and a device therefor.

BACKGROUND ART

As an example of a mobile communication system to which the presentinvention is applicable, a 3rd Generation Partnership Project Long TermEvolution (hereinafter, referred to as LTE) communication system isdescribed in brief.

FIG. 1 is a view schematically illustrating a network structure of anE-UMTS as an exemplary radio communication system. An Evolved UniversalMobile Telecommunications System (E-UMTS) is an advanced version of aconventional Universal Mobile Telecommunications System (UMTS) and basicstandardization thereof is currently underway in the 3GPP. E-UMTS may begenerally referred to as a Long Term Evolution (LTE) system. For detailsof the technical specifications of the UMTS and E-UMTS, reference can bemade to Release 7 and Release 8 of “3rd Generation Partnership Project;Technical Specification Group Radio Access Network”.

Referring to FIG. 1, the E-UMTS includes a User Equipment (UE), eNode Bs(eNBs), and an Access Gateway (AG) which is located at an end of thenetwork (E-UTRAN) and connected to an external network. The eNBs maysimultaneously transmit multiple data streams for a broadcast service, amulticast service, and/or a unicast service.

One or more cells may exist per eNB. The cell is set to operate in oneof bandwidths such as 1.25, 2.5, 5, 10, 15, and 20 MHz and provides adownlink (DL) or uplink (UL) transmission service to a plurality of UEsin the bandwidth. Different cells may be set to provide differentbandwidths. The eNB controls data transmission or reception to and froma plurality of UEs. The eNB transmits DL scheduling information of DLdata to a corresponding UE so as to inform the UE of a time/frequencydomain in which the DL data is supposed to be transmitted, coding, adata size, and hybrid automatic repeat and request (HARQ)-relatedinformation. In addition, the eNB transmits UL scheduling information ofUL data to a corresponding UE so as to inform the UE of a time/frequencydomain which may be used by the UE, coding, a data size, andHARQ-related information. An interface for transmitting user traffic orcontrol traffic may be used between eNBs. A core network (CN) mayinclude the AG and a network node or the like for user registration ofUEs. The AG manages the mobility of a UE on a tracking area (TA) basis.One TA includes a plurality of cells.

Although wireless communication technology has been developed to LTEbased on wideband code division multiple access (WCDMA), the demands andexpectations of users and service providers are on the rise. Inaddition, considering other radio access technologies under development,new technological evolution is required to secure high competitivenessin the future. Decrease in cost per bit, increase in serviceavailability, flexible use of frequency bands, a simplified structure,an open interface, appropriate power consumption of UEs, and the likeare required.

DISCLOSURE Technical Problem

An object of the present invention devised to solve the problem lies ina method and device for performing a HARQ operation in a carrieraggregation with at least one SCell operating in an unlicensed spectrum.

The technical problems solved by the present invention are not limitedto the above technical problems and those skilled in the art mayunderstand other technical problems from the following description.

Technical Solution

The object of the present invention can be achieved by providing amethod for User Equipment (UE) operating in a wireless communicationsystem as set forth in the appended claims.

In another aspect of the present invention, provided herein is acommunication apparatus as set forth in the appended claims.

It is to be understood that both the foregoing general description andthe following detailed description of the present invention areexemplary and explanatory and are intended to provide furtherexplanation of the invention as claimed.

Advantageous Effects

According to the present invention, the UE uses different maxHARQ-Tx andmaxHARQ-Msg3Tx for Licensed band (L-band) HARQ processes and Unlicensedband (U-band) HARQ processes.

It will be appreciated by persons skilled in the art that the effectsachieved by the present invention are not limited to what has beenparticularly described hereinabove and other advantages of the presentinvention will be more clearly understood from the following detaileddescription taken in conjunction with the accompanying drawings.

DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate embodiment(s) of the invention andtogether with the description serve to explain the principle of theinvention.

FIG. 1 is a diagram showing a network structure of an Evolved UniversalMobile Telecommunications System (E-UMTS) as an example of a wirelesscommunication system;

FIG. 2A is a block diagram illustrating network structure of an evolveduniversal mobile telecommunication system (E-UMTS), and FIG. 2B is ablock diagram depicting architecture of a typical E-UTRAN and a typicalEPC;

FIG. 3 is a diagram showing a control plane and a user plane of a radiointerface protocol between a UE and an E-UTRAN based on a 3rd generationpartnership project (3GPP) radio access network standard;

FIG. 4 is a view showing an example of a physical channel structure usedin an E-UMTS system;

FIG. 5 is a block diagram of a communication apparatus according to anembodiment of the present invention;

FIG. 6 illustrates an example of CCs and CA in the LTE-A system, whichare used in embodiments of the present disclosure;

FIG. 7 is a diagram for exemplary Licensed-Assisted Access (LAA)scenarios;

FIG. 8 is an example of LBT operation of a Frame Based Equipment (FBE);

FIG. 9A is an illustration of the CCA check procedure for FBE; and FIG.9B is an illustration of the CCA check and backoff procedures for LBE;

FIG. 10A is a diagram for State Transition Diagram for a LAA eNB, FIG.10B is a diagram for Passive State operations for FBE and LBE, FIG. 10Cis a diagram for Active State operations for LBE, and 10D is a diagramfor Active State operations for FBE;

FIG. 11 is a diagram for MAC structure overview in a UE side; and

FIG. 12 is an example for performing a HARQ operation in a carrieraggregation with at least one SCell operating in an unlicensed spectrumaccording to embodiments of the present invention.

BEST MODE

Universal mobile telecommunications system (UMTS) is a 3rd Generation(3G) asynchronous mobile communication system operating in wideband codedivision multiple access (WCDMA) based on European systems, globalsystem for mobile communications (GSM) and general packet radio services(GPRS). The long-term evolution (LTE) of UMTS is under discussion by the3rd generation partnership project (3GPP) that standardized UMTS.

The 3GPP LTE is a technology for enabling high-speed packetcommunications. Many schemes have been proposed for the LTE objectiveincluding those that aim to reduce user and provider costs, improveservice quality, and expand and improve coverage and system capacity.The 3G LTE requires reduced cost per bit, increased serviceavailability, flexible use of a frequency band, a simple structure, anopen interface, and adequate power consumption of a terminal as anupper-level requirement.

Hereinafter, structures, operations, and other features of the presentinvention will be readily understood from the embodiments of the presentinvention, examples of which are illustrated in the accompanyingdrawings. Embodiments described later are examples in which technicalfeatures of the present invention are applied to a 3GPP system.

Although the embodiments of the present invention are described using along term evolution (LTE) system and a LTE-advanced (LTE-A) system inthe present specification, they are purely exemplary. Therefore, theembodiments of the present invention are applicable to any othercommunication system corresponding to the above definition. In addition,although the embodiments of the present invention are described based ona frequency division duplex (FDD) scheme in the present specification,the embodiments of the present invention may be easily modified andapplied to a half-duplex FDD (H-FDD) scheme or a time division duplex(TDD) scheme.

FIG. 2A is a block diagram illustrating network structure of an evolveduniversal mobile telecommunication system (E-UMTS). The E-UMTS may bealso referred to as an LTE system. The communication network is widelydeployed to provide a variety of communication services such as voice(VoIP) through IMS and packet data.

As illustrated in FIG. 2A, the E-UMTS network includes an evolved UMTSterrestrial radio access network (E-UTRAN), an Evolved Packet Core (EPC)and one or more user equipment. The E-UTRAN may include one or moreevolved NodeB (eNodeB) 20, and a plurality of user equipment (UE) 10 maybe located in one cell. One or more E-UTRAN mobility management entity(MME)/system architecture evolution (SAE) gateways 30 may be positionedat the end of the network and connected to an external network.

As used herein, “downlink” refers to communication from eNodeB 20 to UE10, and “uplink” refers to communication from the UE to an eNodeB. UE 10refers to communication equipment carried by a user and may be alsoreferred to as a mobile station (MS), a user terminal (UT), a subscriberstation (SS) or a wireless device.

FIG. 2B is a block diagram depicting architecture of a typical E-UTRANand a typical EPC.

As illustrated in FIG. 2B, an eNodeB 20 provides end points of a userplane and a control plane to the UE 10. MME/SAE gateway 30 provides anend point of a session and mobility management function for UE 10. TheeNodeB and MME/SAE gateway may be connected via an S1 interface.

The eNodeB 20 is generally a fixed station that communicates with a UE10, and may also be referred to as a base station (BS) or an accesspoint. One eNodeB 20 may be deployed per cell. An interface fortransmitting user traffic or control traffic may be used between eNodeBs20.

The MME provides various functions including NAS signaling to eNodeBs20, NAS signaling security, AS Security control, Inter CN node signalingfor mobility between 3GPP access networks, Idle mode UE Reachability(including control and execution of paging retransmission), TrackingArea list management (for UE in idle and active mode), PDN GW andServing GW selection, MME selection for handovers with MME change, SGSNselection for handovers to 2G or 3G 3GPP access networks, Roaming,Authentication, Bearer management functions including dedicated bearerestablishment, Support for PWS (which includes ETWS and CMAS) messagetransmission. The SAE gateway host provides assorted functions includingPer-user based packet filtering (by e.g. deep packet inspection), LawfulInterception, UE IP address allocation, Transport level packet markingin the downlink, UL and DL service level charging, gating and rateenforcement, DL rate enforcement based on APN-AMBR. For clarity MME/SAEgateway 30 will be referred to herein simply as a “gateway,” but it isunderstood that this entity includes both an MME and an SAE gateway.

A plurality of nodes may be connected between eNodeB 20 and gateway 30via the S1 interface. The eNodeBs 20 may be connected to each other viaan X2 interface and neighboring eNodeBs may have a meshed networkstructure that has the X2 interface.

As illustrated, eNodeB 20 may perform functions of selection for gateway30, routing toward the gateway during a Radio Resource Control (RRC)activation, scheduling and transmitting of paging messages, schedulingand transmitting of Broadcast Channel (BCCH) information, dynamicallocation of resources to UEs 10 in both uplink and downlink,configuration and provisioning of eNodeB measurements, radio bearercontrol, radio admission control (RAC), and connection mobility controlin LTE_ACTIVE state. In the EPC, and as noted above, gateway 30 mayperform functions of paging origination, LTE-IDLE state management,ciphering of the user plane, System Architecture Evolution (SAE) bearercontrol, and ciphering and integrity protection of Non-Access Stratum(NAS) signaling.

The EPC includes a mobility management entity (MME), a serving-gateway(S-GW), and a packet data network-gateway (PDN-GW). The MME hasinformation about connections and capabilities of UEs, mainly for use inmanaging the mobility of the UEs. The S-GW is a gateway having theE-UTRAN as an end point, and the PDN-GW is a gateway having a packetdata network (PDN) as an end point.

FIG. 3 is a diagram showing a control plane and a user plane of a radiointerface protocol between a UE and an E-UTRAN based on a 3GPP radioaccess network standard. The control plane refers to a path used fortransmitting control messages used for managing a call between the UEand the E-UTRAN. The user plane refers to a path used for transmittingdata generated in an application layer, e.g., voice data or Internetpacket data.

A physical (PHY) layer of a first layer provides an information transferservice to a higher layer using a physical channel. The PHY layer isconnected to a medium access control (MAC) layer located on the higherlayer via a transport channel. Data is transported between the MAC layerand the PHY layer via the transport channel Data is transported betweena physical layer of a transmitting side and a physical layer of areceiving side via physical channels. The physical channels use time andfrequency as radio resources. In detail, the physical channel ismodulated using an orthogonal frequency division multiple access (OFDMA)scheme in downlink and is modulated using a single carrier frequencydivision multiple access (SC-FDMA) scheme in uplink.

The MAC layer of a second layer provides a service to a radio linkcontrol (RLC) layer of a higher layer via a logical channel. The RLClayer of the second layer supports reliable data transmission. Afunction of the RLC layer may be implemented by a functional block ofthe MAC layer. A packet data convergence protocol (PDCP) layer of thesecond layer performs a header compression function to reduceunnecessary control information for efficient transmission of anInternet protocol (IP) packet such as an IP version 4 (IPv4) packet oran IP version 6 (IPv6) packet in a radio interface having a relativelysmall bandwidth.

A radio resource control (RRC) layer located at the bottom of a thirdlayer is defined only in the control plane. The RRC layer controlslogical channels, transport channels, and physical channels in relationto configuration, re-configuration, and release of radio bearers (RBs).An RB refers to a service that the second layer provides for datatransmission between the UE and the E-UTRAN. To this end, the RRC layerof the UE and the RRC layer of the E-UTRAN exchange RRC messages witheach other.

One cell of the eNB is set to operate in one of bandwidths such as 1.25,2.5, 5, 10, 15, and 20 MHz and provides a downlink or uplinktransmission service to a plurality of UEs in the bandwidth. Differentcells may be set to provide different bandwidths.

Downlink transport channels for transmission of data from the E-UTRAN tothe UE include a broadcast channel (BCH) for transmission of systeminformation, a paging channel (PCH) for transmission of paging messages,and a downlink shared channel (SCH) for transmission of user traffic orcontrol messages. Traffic or control messages of a downlink multicast orbroadcast service may be transmitted through the downlink SCH and mayalso be transmitted through a separate downlink multicast channel (MCH).

Uplink transport channels for transmission of data from the UE to theE-UTRAN include a random access channel (RACH) for transmission ofinitial control messages and an uplink SCH for transmission of usertraffic or control messages. Logical channels that are defined above thetransport channels and mapped to the transport channels include abroadcast control channel (BCCH), a paging control channel (PCCH), acommon control channel (CCCH), a multicast control channel (MCCH), and amulticast traffic channel (MTCH).

FIG. 4 is a view showing an example of a physical channel structure usedin an E-UMTS system. A physical channel includes several subframes on atime axis and several subcarriers on a frequency axis. Here, onesubframe includes a plurality of symbols on the time axis. One subframeincludes a plurality of resource blocks and one resource block includesa plurality of symbols and a plurality of subcarriers. In addition, eachsubframe may use certain subcarriers of certain symbols (e.g., a firstsymbol) of a subframe for a physical downlink control channel (PDCCH),that is, an L1/L2 control channel In FIG. 4, an L1/L2 controlinformation transmission area (PDCCH) and a data area (PDSCH) are shown.In one embodiment, a radio frame of 10 ms is used and one radio frameincludes 10 subframes. In addition, one subframe includes twoconsecutive slots. The length of one slot may be 0.5 ms. In addition,one subframe includes a plurality of OFDM symbols and a portion (e.g., afirst symbol) of the plurality of OFDM symbols may be used fortransmitting the L1/L2 control information. A transmission time interval(TTI) which is a unit time for transmitting data is 1 ms.

A base station and a UE mostly transmit/receive data via a PDSCH, whichis a physical channel, using a DL-SCH which is a transmission channel,except a certain control signal or certain service data. Informationindicating to which UE (one or a plurality of UEs) PDSCH data istransmitted and how the UE receive and decode PDSCH data is transmittedin a state of being included in the PDCCH.

For example, in one embodiment, a certain PDCCH is CRC-masked with aradio network temporary identity (RNTI) “A” and information about datais transmitted using a radio resource “B” (e.g., a frequency location)and transmission format information “C” (e.g., a transmission blocksize, modulation, coding information or the like) via a certainsubframe. Then, one or more UEs located in a cell monitor the PDCCHusing its RNTI information. And, a specific UE with RNTI “A” reads thePDCCH and then receive the PDSCH indicated by B and C in the PDCCHinformation.

FIG. 5 is a block diagram of a communication apparatus according to anembodiment of the present invention.

The apparatus shown in FIG. 5 can be a user equipment (UE) and/or eNBadapted to perform the above mechanism, but it can be any apparatus forperforming the same operation.

As shown in FIG. 5, the apparatus may comprises a DSP/microprocessor(110) and RF module (transmiceiver; 135). The DSP/microprocessor (110)is electrically connected with the transciver (135) and controls it. Theapparatus may further include power management module (105), battery(155), display (115), keypad (120), SIM card (125), memory device (130),speaker (145) and input device (150), based on its implementation anddesigner's choice.

Specifically, FIG. 5 may represent a UE comprising a receiver (135)configured to receive a request message from a network, and atransmitter (135) configured to transmit the transmission or receptiontiming information to the network. These receiver and the transmittercan constitute the transceiver (135). The UE further comprises aprocessor (110) connected to the transceiver (135: receiver andtransmitter).

Also, FIG. 5 may represent a network apparatus comprising a transmitter(135) configured to transmit a request message to a UE and a receiver(135) configured to receive the transmission or reception timinginformation from the UE. These transmitter and receiver may constitutethe transceiver (135). The network further comprises a processor (110)connected to the transmitter and the receiver. This processor (110) maybe configured to calculate latency based on the transmission orreception timing information.

FIG. 6 illustrates an example of CCs and CA in the LTE-A system, whichare used in embodiments of the present disclosure.

A 3GPP LTE system (conforming to Rel-8 or Rel-9) (hereinafter, referredto as an LTE system) uses Multi-Carrier Modulation (MCM) in which asingle Component Carrier (CC) is divided into a plurality of bands. Incontrast, a 3GPP LTE-A system (hereinafter, referred to an LTE-A system)may use CA by aggregating one or more CCs to support a broader systembandwidth than the LTE system. The term CA is interchangeably used withcarrier combining, multi-CC environment, or multi-carrier environment.

In the present disclosure, multi-carrier means CA (or carriercombining). Herein, CA covers aggregation of contiguous carriers andaggregation of non-contiguous carriers. The number of aggregated CCs maybe different for a DL and a UL. If the number of DL CCs is equal to thenumber of UL CCs, this is called symmetric aggregation. If the number ofDL CCs is different from the number of UL CCs, this is called asymmetricaggregation. The term CA is interchangeable with carrier combining,bandwidth aggregation, spectrum aggregation, etc.

The LTE-A system aims to support a bandwidth of up to 100 MHz byaggregating two or more CCs, that is, by CA. To guarantee backwardcompatibility with a legacy IMT system, each of one or more carriers,which has a smaller bandwidth than a target bandwidth, may be limited toa bandwidth used in the legacy system.

For example, the legacy 3GPP LTE system supports bandwidths {1.4, 3, 5,10, 15, and 20 MHz} and the 3GPP LTE-A system may support a broaderbandwidth than 20 MHz using these LTE bandwidths. A CA system of thepresent disclosure may support CA by defining a new bandwidthirrespective of the bandwidths used in the legacy system.

There are two types of CA, intra-band CA and inter-band CA. Intra-bandCA means that a plurality of DL CCs and/or UL CCs are successive oradjacent in frequency. In other words, the carrier frequencies of the DLCCs and/or UL CCs are positioned in the same band. On the other hand, anenvironment where CCs are far away from each other in frequency may becalled inter-band CA. In other words, the carrier frequencies of aplurality of DL CCs and/or UL CCs are positioned in different bands. Inthis case, a UE may use a plurality of Radio Frequency (RF) ends toconduct communication in a CA environment.

The LTE-A system adopts the concept of cell to manage radio resources.The above-described CA environment may be referred to as a multi-cellenvironment. A cell is defined as a pair of DL and UL CCs, although theUL resources are not mandatory. Accordingly, a cell may be configuredwith DL resources alone or DL and UL resources.

For example, if one serving cell is configured for a specific UE, the UEmay have one DL CC and one UL CC. If two or more serving cells areconfigured for the UE, the UE may have as many DL CCs as the number ofthe serving cells and as many UL CCs as or fewer UL CCs than the numberof the serving cells, or vice versa. That is, if a plurality of servingcells are configured for the UE, a CA environment using more UL CCs thanDL CCs may also be supported.

CA may be regarded as aggregation of two or more cells having differentcarrier frequencies (center frequencies). Herein, the term ‘cell’ shouldbe distinguished from ‘cell’ as a geographical area covered by an eNB.Hereinafter, intra-band CA is referred to as intra-band multi-cell andinter-band CA is referred to as inter-band multi-cell.

In the LTE-A system, a Primacy Cell (PCell) and a Secondary Cell (SCell)are defined. A PCell and an SCell may be used as serving cells. For a UEin RRC_CONNECTED state, if CA is not configured for the UE or the UEdoes not support CA, a single serving cell including only a PCell existsfor the UE. On the contrary, if the UE is in RRC_CONNECTED state and CAis configured for the UE, one or more serving cells may exist for theUE, including a PCell and one or more SCells.

Serving cells (PCell and SCell) may be configured by an RRC parameter. Aphysical-layer ID of a cell, PhysCellId is an integer value ranging from0 to 503. A short ID of an SCell, SCellIndex is an integer value rangingfrom 1 to 7. A short ID of a serving cell (PCell or SCell),ServeCellIndex is an integer value ranging from 1 to 7. IfServeCellIndex is 0, this indicates a PCell and the values ofServeCellIndex for SCells are pre-assigned. That is, the smallest cellID (or cell index) of ServeCellIndex indicates a PCell.

A PCell refers to a cell operating in a primary frequency (or a primaryCC). A UE may use a PCell for initial connection establishment orconnection reestablishment. The PCell may be a cell indicated duringhandover. In addition, the PCell is a cell responsible forcontrol-related communication among serving cells configured in a CAenvironment. That is, PUCCH allocation and transmission for the UE maytake place only in the PCell. In addition, the UE may use only the PCellin acquiring system information or changing a monitoring procedure. AnEvolved Universal Terrestrial Radio Access Network (E-UTRAN) may changeonly a PCell for a handover procedure by a higher-layerRRCConnectionReconfiguraiton message including mobilityControlInfo to aUE supporting CA.

An SCell may refer to a cell operating in a secondary frequency (or asecondary CC). Although only one PCell is allocated to a specific UE,one or more SCells may be allocated to the UE. An SCell may beconfigured after RRC connection establishment and may be used to provideadditional radio resources. There is no PUCCH in cells other than aPCell, that is, in SCells among serving cells configured in the CAenvironment.

When the E-UTRAN adds an SCell to a UE supporting CA, the E-UTRAN maytransmit all system information related to operations of related cellsin RRC_CONNECTED state to the UE by dedicated signaling. Changing systeminformation may be controlled by releasing and adding a related SCell.Herein, a higher-layer RRCConnectionReconfiguration message may be used.The E-UTRAN may transmit a dedicated signal having a different parameterfor each cell rather than it broadcasts in a related SCell.

After an initial security activation procedure starts, the E-UTRAN mayconfigure a network including one or more SCells by adding the SCells toa PCell initially configured during a connection establishmentprocedure. In the CA environment, each of a PCell and an SCell mayoperate as a CC. Hereinbelow, a Primary CC (PCC) and a PCell may be usedin the same meaning and a Secondary CC (SCC) and an SCell may be used inthe same meaning in embodiments of the present disclosure.

FIG. 6(a) illustrates a single carrier structure in the LTE system.There are a DL CC and a UL CC and one CC may have a frequency range of20 MHz.

FIG. 6(b) illustrates a CA structure in the LTE-A system. In theillustrated case of FIG. 6(b), three CCs each having 20 MHz areaggregated. While three DL CCs and three UL CCs are configured, thenumbers of DL CCs and UL CCs are not limited. In CA, a UE may monitorthree CCs simultaneously, receive a DL signal/DL data in the three CCs,and transmit a UL signal/UL data in the three CCs.

If a specific cell manages N DL CCs, the network may allocate M (M≦N) DLCCs to a UE. The UE may monitor only the M DL CCs and receive a DLsignal in the M DL CCs. The network may prioritize L (L≦M≦N) DL CCs andallocate a main DL CC to the UE. In this case, the UE should monitor theL DL CCs. The same thing may apply to UL transmission.

The linkage between the carrier frequencies of DL resources (or DL CCs)and the carrier frequencies of UL resources (or UL CCs) may be indicatedby a higher-layer message such as an RRC message or by systeminformation. For example, a set of DL resources and UL resources may beconfigured based on linkage indicated by System Information Block Type 2(SIB2). Specifically, DL-UL linkage may refer to a mapping relationshipbetween a DL CC carrying a PDCCH with a UL grant and a UL CC using theUL grant, or a mapping relationship between a DL CC (or a UL CC)carrying HARQ data and a UL CC (or a DL CC) carrying an HARQ ACK/NACKsignal.

FIG. 7 is a diagram for exemplary Licensed-Assisted Access (LAA)scenarios.

Carrier aggregation with at least one SCell operating in the unlicensedspectrum is referred to as Licensed-Assisted Access (LAA). In LAA, theconfigured set of serving cells for a UE therefore always includes atleast one SCell operating in the unlicensed spectrum, also called LAASCell. Unless otherwise specified, LAA SCells act as regular SCells andare limited to downlink transmissions in this release.

If the absence of IEEE802.11n/11ac devices sharing the carrier cannot beguaranteed on a long term basis (e.g., by level of regulation), and forthis release if the maximum number of unlicensed channels that E-UTRANcan simultaneously transmit on is equal to or less than 4, the maximumfrequency separation between any two carrier center frequencies on whichLAA SCell transmissions are performed should be less than or equal to 62MHz. The UE is required to support frequency separation in accordancewith 36.133.

LAA eNB applies Listen-Before-Talk (LBT) before performing atransmission on LAA SCell. When LBT is applied, the transmitter listensto/senses the channel to determine whether the channel is free or busy.If the channel is determined to be free, the transmitter may perform thetransmission; otherwise, it does not perform the transmission. If an LAAeNB uses channel access signals of other technologies for the purpose ofLAA channel access, it shall continue to meet the LAA maximum energydetection threshold requirement. The unlicensed band can be used for aWi-Fi band or a Bluetooth band.

It has been agreed that the LTE CA framework is reused as the baselinefor LAA, and that the unlicensed carrier can only be configured asSCell. The SCell over unlicensed spectrum may be downlink only orbi-directional with DL only scenario being prioritized in the SI. LAAonly applies to the operator deployed small cells. Coexistence and fairsharing with other technologies is an essential requirement for LAA inall regions.

Regarding FIG. 7, LAA targets the carrier aggregation operation in whichone or more low power SCells operate in unlicensed spectrum. LAAdeployment scenarios encompass scenarios with and without macrocoverage, both outdoor and indoor small cell deployments, and bothco-location and non-co-location (with ideal backhaul) between licensedand unlicensed carriers. FIG. 7 shows four LAA deployment scenarios,where the number of licensed carriers and the number of unlicensedcarriers can be one or more. As long as the unlicensed small celloperates in the context of the carrier aggregation, the backhaul betweensmall cells can be ideal or non-ideal. In scenarios where carrieraggregation is operated within the small cell with carriers in both thelicensed and unlicensed bands, the backhaul between macro cell and smallcell can be ideal or non-ideal.

Scenario 1: Carrier aggregation between licensed macro cell (F1) andunlicensed small cell (F3).

Scenario 2: Carrier aggregation between licensed small cell (F2) andunlicensed small cell (F3) without macro cell coverage.

Scenario 3: Licensed macro cell and small cell (F1), with carrieraggregation between licensed small cell (F1) and unlicensed small cell(F3).

Scenario 4: Licensed macro cell (F1), licensed small cell (F2) andunlicensed small cell (F3). In this case, there is Carrier aggregationbetween licensed small cell (F2) and unlicensed small cell (F3). Ifthere is ideal backhaul between macro cell and small cell, there can becarrier aggregation between macro cell (F1), licensed small cell (F2)and unlicensed small cell (F3). If dual connectivity is enabled, therecan be dual connectivity between macro cell and small cell.

In the study to support deployment in unlicensed spectrum for the abovescenarios, CA functionalities are used as a baseline to aggregatePCell/PSCell on licensed carrier and SCell on unlicensed carrier. Whennon-ideal backhaul is applied between a Macro cell and a small cellcluster in the Scenarios 3 and 4, small cell on unlicensed carrier hasto be aggregated with a small cell on licensed carrier in the small cellcluster through ideal backhaul. The focus is to identify the need ofand, if necessary, evaluate needed enhancements to the LTE RAN protocolsapplicable to the carrier aggregation in all the above scenarios.

FIG. 8 is an example of LBT operation of a Frame Based Equipment (FBE).

The Listen-Before-Talk (LBT) procedure is defined as a mechanism bywhich an equipment applies a clear channel assessment (CCA) check beforeusing the channel The CCA utilizes at least energy detection todetermine the presence or absence of other signals on a channel in orderto determine if a channel is occupied or clear, respectively. Europeanand Japanese regulations mandate the usage of LBT in the unlicensedbands. Apart from regulatory requirements, carrier sensing via LBT isone way for fair sharing of the unlicensed spectrum and hence it isconsidered to be a vital feature for fair and friendly operation in theunlicensed spectrum in a single global solution framework.

According to ETSI regulation (EN 301 893 V1.7.1) of the Europe, two LBToperations respectively referred to as a FBE (Frame Based Equipment) andan LBE (Load Based Equipment) are shown as an example. The FBEcorresponds to an equipment where the transmit/receive structure is notdirectly demand-driven but has fixed timing and the LBE corresponds toan equipment where the transmit/receive structure is not fixed in timebut demand-driven.

The FBE configures a fixed frame using channel occupancy time (e.g.,1˜10 ms) corresponding to time capable of lasting transmission when acommunication node has succeeded in channel access and an idle periodcorresponding to minimum 5% of the channel occupancy time. CCA isdefined by an operation of monitoring a channel during a CCS slot(minimum 20 μs) at an end part of the idle period.

In this case, a communication node periodically performs the CCA in afixed frame unit. If a channel is in an unoccupied state, thecommunication node transmits data during the channel occupancy time. Ifa channel is in an occupied state, the communication node postpones datatransmission and waits until a CCA slot of a next period.

A CCA (clear channel assessment) check and backoff mechanism are two keycomponents of channel evaluation stage. FIG. 9A illustrates the CCAcheck procedure for FBE, in which no backoff mechanism is needed. FIG.9A illustrates the CCA check and backoff procedure for LBE.

In order to deploy LAA eNB in regions where LBT is required, LAA eNBshall comply with LBT requirements in those regions. In addition, theLBT procedures shall be specified such that fair sharing of theunlicensed spectrum may be achieved between LAA devices themselves andamong LAA and other technologies, e.g. WiFi.

After eNB acquires the unlicensed spectrum through LBT proceduresuccessfully, it may notify its UEs the result so that preparations maybe made accordingly for transmission, e.g., UE may start measurements.

CCA check (FBE and LBE) and backoff mechanism (LBE) are two majorcomponents of LBT operation, and thus are worth further clarification orstudy in order to fulfil LBT requirement efficiently in LAA system.Since the LBT procedure is in preparation for transmitting data orsignals over unlicensed channel, it is straightforward that both MAC andPHY layers are closely involved in the LBT process. FIGS. 10A to 10Dillustrate our views on the interaction and function split between MACand PHY during the CCA check and backoff operations. They can be used tohelp identify the potential impacts that LBT requirements brought toRAN2.

FIG. 10A is a diagram for State Transition Diagram for a LAA eNB, FIG.10B is a diagram for Passive State operations for FBE and LBE, FIG. 10Cis a diagram for Active State operations for LBE, and 10D is a diagramfor Active State operations for FBE.

An LAA eNB operating status is classified as in either Active State orPassive State, as shown in FIG. 10A.

The passive state means that an LAA eNB has no need of utilizingunlicensed channels, and the active state means that an LAA eNB is inneed of unlicensed resources. The transition from Passive State toActive State is triggered when radio resources over unlicensed channelis needed.

FIG. 10B depicts the operation in Passive State in more details, and isapplicable to both FBE and LBE. The transition from Active State toPassive State occurs when there is no more need of unlicensed channel.

FIG. 10C outlines the operation in Active State, assuming LBE Option Brequirements.

As shown in the FIG. 10C, PHY checks the availability of unlicensedchannel and transmits (steps 1 b, 2 b, 3 b and 6 b), while MAC makes thescheduling decision and decides whether radio resources over unlicensedcarrier is needed (steps 4 b and 7 b). In addition, MAC also generatesbackoff counter N (step 5 b).

It is worth pointing out that scheduling decision in 4 b and 7 bconsiders both licensed and unlicensed channel resources. User data canbe directed for transmission on either licensed or unlicensed channelWhen MAC evaluates the demand for unlicensed channel resources (steps 4b and 7 b), it may take PHY's need into consideration, e.g., whether DRSwill be transmitted soon. Step 3 b includes not only the time eNBtransmits data over the unlicensed channel, but also the idle periodthat is required to fulfil LBT requirements, as well as the shortcontrol signalling transmission duration. The initial CCA check (step 2b) is triggered by the demand for unlicensed channel resources, such asMAC data and/or PHY signalling. This is in line with “demand-driven”definition of LBE.

For ECCA check (steps 5 b and 6 b), MAC provides the backoff counter Nand PHY is in charge of starting and performing CCA check in each of theN ECCA slots. The reason of letting MAC but not PHY generate backoffcounter value N is that the MAC scheduler has the betterknowledge/prediction regarding the availability of data that may betransmitted or offloaded over unlicensed carrier(s). In addition, theknowledge of value N will help MAC scheduler predict buffering delay tosome extent. At the end of a failed ECCA and before PHY starts a newround of ECCA, it is reasonable for PHY to check with MAC first whetherthere is still any need to access the resources of unlicensed channel IfMAC scheduler prefers to use licensed carriers for data transmissions inthe next several subframes, or if MAC empties its buffer already, thereis no point for PHY to start a new round of ECCA. Because of thenecessity of checking with MAC (step 4 b) and the benefit of MAC knowingN value, it is preferred that MAC provides the backoff counter N to PHY.

FIG. 10D outlines the operation in Active State following FBErequirements. Interpretation of each step is similar to that in FIG.10C.

FIG. 11 is a diagram for MAC structure overview in a UE side.

The MAC layer handles logical-channel multiplexing, hybrid-ARQretransmissions, and uplink and downlink scheduling. It is alsoresponsible for multiplexing/demultiplexing data across multiplecomponent carriers when carrier aggregation is used.

The MAC provides services to the RLC in the form of logical channels. Alogical channel is defined by the type of information it carries and isgenerally classified as a control channel, used for transmission ofcontrol and configuration information necessary for operating an LTEsystem, or as a traffic channel, used for the user data. The set oflogical channel types specified for LTE includes Broadcast ControlChannel (BCCH), Paging Control Channel (PCCH), Common Control Channel(CCCH), Dedicated Control Channel (DCCH), Multicast Control Channel(MCCH), Dedicated Traffic Channel (DTCH), Multicast Traffic Channel(MTCH).

From the physical layer, the MAC layer uses services in the form oftransport channels. A transport channel is defined by how and with whatcharacteristics the information is transmitted over the radio interface.Data on a transport channel is organized into transport blocks. In eachTransmission Time Interval (TTI), at most one transport block of dynamicsize is transmitted over the radio interface to/from a terminal in theabsence of spatial multiplexing. In the case of spatial multiplexing(MIMO), there can be up to two transport blocks per TTI.

Associated with each transport block is a Transport Format (TF),specifying how the transport block is to be transmitted over the radiointerface. The transport format includes information about thetransport-block size, the modulation-and-coding scheme, and the antennamapping. By varying the transport format, the MAC layer can thus realizedifferent data rates. Rate control is therefore also known astransport-format selection.

To support priority handling, multiple logical channels, where eachlogical channel has its own RLC entity, can be multiplexed into onetransport channel by the MAC layer. At the receiver, the MAC layerhandles the corresponding demultiplexing and forwards the RLC PDUs totheir respective RLC entity for in-sequence delivery and the otherfunctions handled by the RLC. To support the demultiplexing at thereceiver, a MAC is used. To each RLC PDU, there is an associatedsub-header in the MAC header. The sub-header contains the identity ofthe logical channel (LCID) from which the RLC PDU originated and thelength of the PDU in bytes. There is also a flag indicating whether thisis the last sub-header or not. One or several RLC PDUs, together withthe MAC header and, if necessary, padding to meet the scheduledtransport-block size, form one transport block which is forwarded to thephysical layer.

In addition to multiplexing of different logical channels, the MAC layercan also insert the so-called MAC control elements into the transportblocks to be transmitted over the transport channels. A MAC controlelement is used for inband control signaling—for example, timing-advancecommands and random-access response. Control elements are identifiedwith reserved values in the LCID field, where the LCID value indicatesthe type of control information.

Furthermore, the length field in the sub-header is removed for controlelements with a fixed length.

The MAC multiplexing functionality is also responsible for handling ofmultiple component carriers in the case of carrier aggregation. Thebasic principle for carrier aggregation is independent processing of thecomponent carriers in the physical layer, including control signaling,scheduling and HARQ retransmissions, while carrier aggregation isinvisible to RLC and PDCP. Carrier aggregation is therefore mainly seenin the MAC layer, where logical channels, including any MAC controlelements, are multiplexed to form one (two in the case of spatialmultiplexing) transport block(s) per component carrier with eachcomponent carrier having its own HARQ entity.

There is one HARQ entity at the MAC entity for each Serving Cell withconfigured uplink, which maintains a number of parallel HARQ processesallowing transmissions to take place continuously while waiting for theHARQ feedback on the successful or unsuccessful reception of previoustransmissions.

When the physical layer is configured for uplink spatial multiplexing,there are two HARQ processes associated with a given TTI. Otherwisethere is one HARQ process associated with a given TTI.

At a given TTI, if an uplink grant is indicated for the TTI, the HARQentity identifies the HARQ processes for which a transmission shouldtake place. It also routes the received HARQ feedback (ACK/NACKinformation), MCS and resource, relayed by the physical layer, to theappropriate HARQ processes.

For each TTI, the HARQ entity shall identify the HARQ processesassociated with this TTI. And for each identified HARQ process, if anuplink grant has been indicated for this process and this TTI:

if the received grant was not addressed to a Temporary C-RNTI on PDCCHand if the NDI provided in the associated HARQ information has beentoggled compared to the value in the previous transmission of this HARQprocess; or

if the uplink grant was received on PDCCH for the C-RNTI and the HARQbuffer of the identified process is empty; or

if the uplink grant was received in a Random Access Response, the UEshall obtain the MAC PDU to transmit from the Msg3 buffer if there is aMAC PDU in the Msg3 buffer and the uplink grant was received in a RandomAccess Response. Or, the UE shall obtain the MAC PDU to transmit fromthe “Multiplexing and assembly” entity if there isn't the MAC PDU in theMsg3 buffer and the uplink grant was received in the Random AccessResponse.

And the UE shall deliver the MAC PDU and the uplink grant and the HARQinformation to the identified HARQ process, and instruct the identifiedHARQ process to trigger a new transmission.

Else, the UE shall deliver the uplink grant and the HARQ information(redundancy version) to the identified HARQ process, and instruct theidentified HARQ process to generate an adaptive retransmission.

Else, if the HARQ buffer of this HARQ process is not empty, the UE shallinstruct the identified HARQ process to generate a non-adaptiveretransmission.

When determining if NDI has been toggled compared to the value in theprevious transmission the MAC entity shall ignore NDI received in alluplink grants on PDCCH for its Temporary C-RNTI.

Each HARQ process is associated with a HARQ buffer.

Each HARQ process shall maintain a state variable CURRENT_TX_NB, whichindicates the number of transmissions that have taken place for the MACPDU currently in the buffer, and a state variable HARQ_FEEDBACK, whichindicates the HARQ feedback for the MAC PDU currently in the buffer.When the HARQ process is established, CURRENT_TX_NB shall be initializedto 0.

The sequence of redundancy versions is 0, 2, 3, 1. The variableCURRENT_IRV is an index into the sequence of redundancy versions. Thisvariable is up-dated modulo 4.

New transmissions are performed on the resource and with the MCSindicated on PDCCH or Random Access Response. Adaptive retransmissionsare performed on the resource and, if provided, with the MCS indicatedon PDCCH. Non-adaptive retransmission is performed on the same resourceand with the same MCS as was used for the last made transmissionattempt.

The MAC entity is configured with a Maximum number of HARQ transmissionsand a Maximum number of Msg3 HARQ transmissions by RRC: maxHARQ-Tx andmaxHARQ-Msg3Tx respectively. For transmissions on all HARQ processes andall logical channels except for transmission of a MAC PDU stored in theMsg3 buffer, the maximum number of transmissions shall be set tomaxHARQ-Tx. For transmission of a MAC PDU stored in the Msg3 buffer, themaximum number of transmissions shall be set to maxHARQ-Msg3Tx.

When the HARQ feedback is received for this TB, the HARQ process shallset HARQ_FEEDBACK to the received value.

If the HARQ entity requests a new transmission, the HARQ process shallset CURRENT_TX_NB to 0, set CURRENT_IRV to 0, store the MAC PDU in theassociated HARQ buffer, store the uplink grant received from the HARQentity, set HARQ_FEEDBACK to NACK, and generate a transmission asdescribed below.

If the HARQ entity requests a retransmission, the HARQ process shallincrement CURRENT_TX_NB by 1. And if the HARQ entity requests anadaptive retransmission, the UE shall store the uplink grant receivedfrom the HARQ entity, set CURRENT_IRV to the index corresponding to theredundancy version value provided in the HARQ information, setHARQ_FEEDBACK to NACK, and generate a transmission as described below.Else if the HARQ entity requests a non-adaptive retransmission, ifHARQ_FEEDBACK=NACK, the UE shall generate a transmission as describedbelow.

To generate a transmission, if the MAC PDU was obtained from the Msg3buffer; or if there is no measurement gap at the time of thetransmission and, in case of retransmission, the retransmission does notcollide with a transmission for a MAC PDU obtained from the Msg3 bufferin this TTI, the HARQ process shall instruct the physical layer togenerate a transmission according to the stored uplink grant with theredundancy version corresponding to the CURRENT_IRV value, incrementCURRENT_IRV by 1. In addition, the UE shall set HARQ_FEEDBACK to ACK atthe time of the HARQ feedback reception for this transmission only ifthere is a measurement gap at the time of the HARQ feedback receptionfor this transmission and if the MAC PDU was not obtained from the Msg3buffer.

After performing above actions, the HARQ process then shall flush theHARQ buffer if CURRENT_TX_NB=maximum number of transmissions−1.

In the prior art, the same value of maxHARQ-Tx and maxHARQ-Msg3Tx areused for all HARQ processes in the UE. The UE maintains a counterCURRENT_TX_NB for each HARQ process to limit the maximum number oftransmission of the MAC PDU transmitted by the HARQ process. The HARQprocess increases its CURRENT_TX_NB by 1 when the HARQ entity requests aretransmission of the MAC PDU to the HARQ process. After that, the HARQprocess instructs the physical layer to generate a transmission of theMAC PDU.

However, in LAA, the channel in unlicensed band may be busy at the timeof transmission, and the physical layer may not perform transmission ofthe MAC PDU on the unlicensed band cell. In this case, the number oftransmission is counted, but the transmission is not performed. Thiswould reduce the probability of transmission on unlicensed band cell.

FIG. 12 is a conceptual diagram for performing a HARQ operation in acarrier aggregation with at least one SCell operating in an unlicensedspectrum according to embodiments of the present invention.

The invention is that the UE uses different maxHARQ-Tx andmaxHARQ-Msg3Tx for Licensed band (L-band) HARQ processes and Unlicensedband (U-band) HARQ processes.

The UE configures with a plurality of cells, wherein each of theplurality of cells belongs to one of a first cell group and a secondcell group (S1201). The first cell group is L-band cells or, the secondcell group is U-band cells.

The UE can receive an indication indicating whether a cell of theplurality of cells belongs to the first cell group and the second cellgroup (S1203). And the UE can also receive an indication indicating theHARQ process is assigned to either the first cell group or the secondcell group (S1205). Thus, the HARQ process can be assigned to either thefirst cell group or the second cell group

When the UE receives two sets of maximum number of Hybrid-ARQ (HARQ)transmission (S1207), wherein a first set is related to a first cellgroup and a second set is related to a second cell group, the UE candetermine which set is configured to a HARQ process.

The eNB configures the UE with two sets of maximum number of HARQtransmission by RRC signaling. The first set for the L-band cellsincludes L-maxHARQ-Tx, L-maxHARQ-Msg3Tx, and the second set for theU-band cells includes U-maxHARQ-Tx, U-maxHARQ-Msg3Tx.

By above mentioned signaling, the UE applies the first set to a HARQprocess if the HARQ process is assigned to the first cell group (S1209)and the UE applies the second set to the HARQ process if the HARQprocess is assigned to the second cell group (S1211).

For transmissions on all HARQ processes and all logical channels exceptfor transmission of a MAC PDU stored in the Msg3 buffer, the UE sets themaximum number of transmissions to L-maxHARQ-Tx for the HARQ processesassigned to L-band cells, and to U-maxHARQ-Tx for the HARQ processesassigned to U-band cells. And for transmission of a MAC PDU stored inthe Msg3 buffer, the UE sets the maximum number of transmissions toL-maxHARQ-Msg3Tx for the HARQ processes assigned to L-band cells, and toU-maxHARQ-Msg3Tx for the HARQ processes assigned to U-band cells.

When the UE applies the first set to a HARQ process if the HARQ processis assigned to the first cell group (S1209), if a HARQ entity requests anew transmission, the HARQ process shall set CURRENT_TX_NB to 0. And Ifthe HARQ entity requests a retransmission, the HARQ process shallincrement CURRENT_TX_NB by 1. When a value of the CURRENT_TX_NB reachesthe maximum number of transmissions (if CURRENT_TX_NB=maximum number oftransmissions−1), the UE shall flush the HARQ buffer. In this case, ifthe HARQ process is assigned to the first group cells, the maximumnumber of transmissions can be L-maxHARQ-Tx, L-maxHARQ-Msg3Tx.

And when the UE applies the second set to the HARQ process if the HARQprocess is assigned to the second cell group (S1211), the maximum numberof transmissions can be U-maxHARQ-Tx, U-maxHARQ-Msg3Tx. So, if a HARQentity requests a new transmission, the HARQ process shall setCURRENT_TX_NB to 0. And If the HARQ entity requests a retransmission,the HARQ process shall increment CURRENT_TX_NB by 1. When a value of theCURRENT_TX_NB reaches the U-maxHARQ-Tx or U-maxHARQ-Msg3Tx, the UE shallflush the HARQ buffer.

Preferably, the maximum number of HARQ transmission for the second setis larger than the maximum number of HARQ transmission for the firstset.

Preferably, the maximum number of HARQ transmission is from 0 toinfinity.

The embodiments of the present invention described hereinbelow arecombinations of elements and features of the present invention. Theelements or features may be considered selective unless otherwisementioned. Each element or feature may be practiced without beingcombined with other elements or features. Further, an embodiment of thepresent invention may be constructed by combining parts of the elementsand/or features. Operation orders described in embodiments of thepresent invention may be rearranged. Some constructions of any oneembodiment may be included in another embodiment and may be replacedwith corresponding constructions of another embodiment. It is obvious tothose skilled in the art that claims that are not explicitly cited ineach other in the appended claims may be presented in combination as anembodiment of the present invention or included as a new claim bysubsequent amendment after the application is filed.

In the embodiments of the present invention, a specific operationdescribed as performed by the BS may be performed by an upper node ofthe BS. Namely, it is apparent that, in a network comprised of aplurality of network nodes including a BS, various operations performedfor communication with an MS may be performed by the BS, or networknodes other than the BS. The term ‘eNB’ may be replaced with the term‘fixed station’, ‘Node B’, ‘Base Station (BS)’, ‘access point’, etc.

The above-described embodiments may be implemented by various means, forexample, by hardware, firmware, software, or a combination thereof.

In a hardware configuration, the method according to the embodiments ofthe present invention may be implemented by one or more ApplicationSpecific Integrated Circuits (ASICs), Digital Signal Processors (DSPs),Digital Signal Processing Devices (DSPDs), Programmable Logic Devices(PLDs), Field Programmable Gate Arrays (FPGAs), processors, controllers,microcontrollers, or microprocessors.

In a firmware or software configuration, the method according to theembodiments of the present invention may be implemented in the form ofmodules, procedures, functions, etc. performing the above-describedfunctions or operations. Software code may be stored in a memory unitand executed by a processor. The memory unit may be located at theinterior or exterior of the processor and may transmit and receive datato and from the processor via various known means.

Those skilled in the art will appreciate that the present invention maybe carried out in other specific ways than those set forth hereinwithout departing from essential characteristics of the presentinvention. The above embodiments are therefore to be construed in allaspects as illustrative and not restrictive. The scope of the inventionshould be determined by the appended claims, not by the abovedescription, and all changes coming within the meaning of the appendedclaims are intended to be embraced therein.

INDUSTRIAL APPLICABILITY

While the above-described method has been described centering on anexample applied to the 3GPP LTE system, the present invention isapplicable to a variety of wireless communication systems in addition tothe 3GPP LTE system.

1. A method for a User Equipment (UE) operating in a wirelesscommunication system, the method comprising: configuring with aplurality of cells, wherein each of the plurality of cells belongs toone of a first cell group and a second cell group; receiving two sets ofmaximum number of Hybrid-ARQ (HARQ) transmission, wherein a first set isrelated to a first cell group and a second set is related to a secondcell group; applying the first set to a HARQ process if the HARQ processis assigned to the first cell group; and applying the second set to theHARQ process if the HARQ process is assigned to the second cell group.2. The method according to claim 1, further comprising: receiving anindication indicating whether a cell of the plurality of cells belongsto the first cell group and the second cell group.
 3. The methodaccording to claim 1, wherein the first set includes a first maxHARQ-Txand a first maxHARQ-Msg3Tx, and the second set includes a secondmaxHARQ-Tx and a second maxHARQ-Msg3Tx.
 4. The method according to claim3, wherein the UE sets a maximum number of HARQ transmissions to thefirst maxHARQ-Tx if the HARQ process is assigned to the first cellgroup, and to the second maxHARQ-Tx if the HARQ process is assigned tothe second cell group, for all transmissions on the HARQ processexceptfor transmission of a MAC PDU stored in the Msg3 buffer.
 5. The methodaccording to claim 3, wherein the UE sets a maximum number of HARQtransmissions to the first maxHARQ-Msg3Tx if the HARQ process isassigned to the first cell group, and to the second maxHARQ-Msg3Tx ifthe HARQ process is assigned to the second cell group, for transmissionof a MAC PDU stored in the Msg3 buffer.
 6. The method according to claim1, wherein all cells in the second cell group operates in unlicensedspectrum.
 7. The method according to claim 6, wherein the maximum numberof HARQ transmission for the second set is larger than the maximumnumber of HARQ transmission for the first set.
 8. The method accordingto claim 1, wherein the maximum number of HARQ transmission is from 0 toinfinity.
 9. The method according to claim 1, wherein the HARQ processis assigned to either the first cell group or the second cell group. 10.A User Equipment (UE) operating in a wireless communication system, theUE comprising: a Radio Frequency (RF) module; and a processor configuredto control the RF module, wherein the processor is configured toconfigure with a plurality of cells, wherein each of the plurality ofcells belongs to one of a first cell group and a second cell group, toreceive two sets of maximum number of Hybrid-ARQ (HARQ) transmission,wherein a first set is related to a first cell group and a second set isrelated to a second cell group, to apply the first set to a HARQ processif the HARQ process is assigned to the first cell group, and to applythe second set to the HARQ process if the HARQ process is assigned tothe second cell group.
 11. The UE according to claim 10, wherein theprocessor is further configured to receive an indication indicatingwhether a cell of the plurality of cells belongs to the first cell groupand the second cell group.
 12. The UE according to claim 10, wherein thefirst set includes a first maxHARQ-Tx and a first maxHARQ-Msg3Tx, andthe second set includes a second maxHARQ-Tx and a second maxHARQ-Msg3Tx13. The UE according to claim 12, wherein the UE sets a maximum numberof HARQ transmissions to the first maxHARQ-Tx if the HARQ process isassigned to the first cell group, and to the second maxHARQ-Tx if theHARQ process is assigned to the second cell group, for all transmissionson the HARQ process except for transmission of a MAC PDU stored in theMsg3 buffer.
 14. The UE according to claim 12, wherein the UE sets amaximum number of HARQ transmissions to the first maxHARQ-Msg3Tx if theHARQ process is assigned to the first cell group, and to the secondmaxHARQ-Msg3Tx if the HARQ process is assigned to the second cell group,for transmission of a MAC PDU stored in the Msg3 buffer.
 15. The UEaccording to claim 10, wherein all cells in the second cell groupoperates in unlicensed spectrum.
 16. The UE according to claim 15,wherein the maximum number of HARQ transmission for the second set islarger than the maximum number of HARQ transmission for the first set.17. The UE according to claim 10, wherein the maximum number of HARQtransmission is from 0 to infinity.
 18. The UE according to claim 10,wherein the HARQ process is assigned to either the first cell group orthe second cell group.